The present invention is directed principally to flat-molded and form-molded (e.g., dip-molded) elastomeric products, formed by the curing of fluid elastomer materials, in which for reasons of functionality and/or aesthetics it is important that different portions, areas, sections or layers of the product be formed of elastomeric materials having different durometers, colors, and/or other material characteristics.
Notable examples of flat-molded products of this type include shoe soles, in which it is desirable to have certain areas with higher durometers for durability and others with lower durometers for cushioning, and logos on athletic clothing, in which it is important that different areas of the article be formed in distinct, often bright colors. Examples of form-molded products, in turn, include gloves and boots, in which again it is often important for certain areas of the product to be formed of materials having different durometers, colors, or other characteristics so as to enhance the function or appearance of the article; for example, it may be advantageous for one section of a glove or boot to be very elastic and pliable while another section is more rigid and puncture-resistant, while yet another section may be specifically configured for traction or cushioning.
In conventional practice, such articles have usually been manufactured using injection molding or compression molding processes. Conventional injection molding processes are capable of using only one color/durometer of material at a time: in products where two or more colors are required, these must be silk-screened or otherwise painted/coated onto the surface of the injection molded part and thus tend to wear off quickly in use. Multi-durometer and multi-color parts can also be created through a compression molding process, which requires that each part of a specific color or durometer be molded separately and then assembled using adhesives and pressure, but this is a very labor-intensive and expensive technique and the pieces often tend to delaminate or otherwise come apart in use.
Another common problem with injection and compression molding is the extreme cost which is inherent in making the molds which are required for these processes (e.g., a production mold can easily cost $50,000 U.S. or more), which makes, for example, seasonal style changes prohibitively expensive. Furthermore, since the materials which are traditionally used in these products and processes are relatively non-elastic in nature, multiple molds are required for different sizes of each product; for example, in the case of shoe soles, separate, specific molds are required for each size and width of foot.
In addition to the problems which have been discussed above, yet another difficulty often develops in the case of close-fitting molded elastomeric products, for example, the waterproof boots and gloves which are widely used in athletic/sports activities such as scuba diving, snow/water skiing, surfing/windsurfing, and so on. Waterproof boots and gloves of this kind are conventionally constructed of shaped rubber-cloth pieces which are sewn together, with the seams then being coated with rubber/sealant to waterproof them. Not only is this process inefficient and labor-intensive, it is very common for the seams to stretch during use, so that the article develops leaks and becomes water logged. As a result, such boots/gloves tend to fill and expand with water (especially under hard use), so that they do not conform properly to the wearer's foot/hand; as a stop-gap measure, such articles are often fitted with zippers (which may create yet another source of leaks) in an effort to allow the boot or glove to be donned/removed while remaining tightly contoured to the ankle or wrist. Also, the seams and zipper can be quite uncomfortable and abrasive to the user's foot.
A one-piece boot, glove or other molded article which incorporates multiple characteristics (e.g., different durometers and/or colors) in different sections or areas, but without requiring the use of adhesives or seams, would solve these problems. Prior art attempts at providing a solution along these lines have not been feasible, however, at least from a commercial standpoint. For example, the following three U.S. patents disclose various waterproof, resilient articles which are adapted to fit various parts of a human body, but the processes which are taught therein are not entirely satisfactory for use in connection with the types of products which have been described above.
For example, U.S. Pat. No. 2,666,208 (Funk) discloses a process for manufacture of prosthetic stockings. The stockings are formed of a sheer fabric base which is coated on one side with alternate layers of rubber-like and filler materials to render the stocking opaque. Funk does not, however, disclose any commercially feasible batch or continuous process for which is capable of forming a seamless elastomeric product having different material characteristics (e.g., different colors or durometers) in various areas or sections.
U.S. Pat. No. 3,633,216 (Schonboltz) discloses a rubber surgical glove which is formed of a relatively thin material so as to provide maximum tactile agility and ease of manipulation. The glove has at least one finger portion which is made with a double thickness to prevent punctures and the passage of contamination therethrough. Schonboltz does not disclose any process for bonding elastomers having different colors, durometers, or other characteristics.
U.S. Pat. No. 4,133,624 (Heavner et al.) discloses a molded glove having hand and wrist portions. The wrist portion includes a plurality of longitudinal channels around the circumference thereof, and also a plurality of circumferential channels at the end opposite the hand portion. The channels cross one another, and the thickness of the glove along the channels is greater than the thickness in adjacent areas; the purpose of the channels is to provide the cuff with improved resistance against rolling down while being worn, as compared with gloves which have only longitudinal flutes/channels or beaded cuffs. The reference does not disclose any process for bonding elastomers having different colors, durometers or other characteristics.
Other known prior art includes the following:
Canadian Patent No. 1,077,263 (Stockli) discloses a boot for aquatic activities. A cellular elastomeric sock is bonded to a non-cellular, in-situ vulcanized outsole which includes a toe portion, a heel portion and foxing. The sock may be covered with a fabric such as nylon. Bonding of the outsole may be aided by applying a first layer of neoprene cement, which penetrates and impregnates the fabric, and a second layer of a natural rubber cement. Vulcanizing of the outsole is carried out in a heated, pressurized environment. Stockli does not disclose any process in which elastomers having different colors, durometers or other characteristics are permanently bonded in the molding process itself.
French Patent No. 2,454,280 (Fritsch) discloses a beach shoe which is made by dipping a hollow mold into latex to produce an elastic, close-fitting shoe having variable wall thickness. Greater wall thicknesses at the sole and at the top, toe and heel areas are produced by using a mold having thicker walls those regions, so that the greater local heat capacity of the mold in these areas results in a greater build-up of gelled latex material. Fritsch does not disclose any process for bonding elastomers having different material characteristics.